One problem with the trust system that would be great to try and solve it retaliation feedback. Often times people are afraid to leave someone who they think is untrustworthy negative feedback because that person has DefaultTrust and a high trust score and they fear retaliation negative feedback. I'm not sure of a good way of mitigating this, but it would be very useful.
IMO, removing the default trust list, and creating some sort of system to have BOTH users agree to a transaction before any trust ratings that can effect your trust score can be left would go a long way in doing this. People would still be able to comment on your trust page with neutrals, but it would not impact your trust rating. This 100% ensures only directly involved individuals in a transaction have the power to damage another persons trust score. Furthermore it may even be good policy to require users post the agreement first and reference during this mutual agreement function it so any disputes can be arbitrated based only upon the agreement the two entered into.